I was going through some of my fly lines on spools, Keep in mind I have not used them for close to 15 years. I have all of them in bags marked with the line type floating, sinking tip and line weights and color.

I found one that is not in a marked bag. I know it is either a 5w or 7w and it is a sink tip line. I was wondering if there is any way to weigh/measure this line to tell what weight it is?

No need to look on the Internet. We have the AFTMA line weights in the FAQ section. Try here.

Weigh the front 30' of line in grains and that will tell you what line it is. If you don't have a scale that weighs in grains you can use any scale that is sensitive enough to measure the first 30' of line. Take a known 5wt and weigh the front 30' and note the measurement on your scale. Now weigh the first 30' of the un-known line on the same scale and compare the measurements. If they weigh the same you have a 5wt and if it is heavier you have a 7wt. You could also compare weigh the un-known line to a known 7wt to verify your results.